How do you weigh someone in a zero gravity space station? Well, you
don't, because their weight is zero. But mass is ever-present and
measuring it can be a difficult proposition without gravity. Currently a
motorized chair on springs is used that measures how a person bounces
when sitting on it.

Researchers from Eurecom in Alpes-Maritimes, France, and the Italian
Institute of Technology's Center for Human Space Robotics in Torino have
developed a method that relies on a Microsoft Kinect 3-D video camera to
calculate the volume of a person in front of it and using statistics to
turn that into an estimated mass measurement.

From the New Scientist:

Then the team ran their calculation using a statistical
model that links weight to body measurements based on a database of
28,000 people. Velardo's [Carmelo Velardo, computer scientist at Eurecom]
estimates are 97 percent accurate, corresponding to an average error
of just 2.7 kilograms, which is comparable to the current method used on
board the ISS.

"This technique appears feasible, although not without some effort,"
says John Charles, chief scientist on NASA's human research program in
Houston, Texas. He says that microgravity shifts water around inside
astronauts' bodies, which means their density may not match the
assumptions in the model.

Charles adds that combining the idea with the existing weighing
system might prove more beneficial, as the Kinect measures body volume
while the stool measures mass.